This invention is generally directed to toner and developer compositions. More specifically, the present invention is directed to positively charged colored toner compositions containing a low molecular weight wax such as polyethylene or polypropylene, and a charging enhancing additive. These compositions are particularly useful for permitting the development of colored images in electrostatographic imaging processes wherein an offset preventing liquid, such as silicon oil is not required.
Developer compositions with charge enhancing additives, especially additives which impart a positive charge to the toner resin, are well known. Thus, for example, there is described in U.S. Pat. No. 2,986,521 reversal developer compositions comprised of toner resin particles coated with finely divided colloidal silica. According to the disclosure of this patent the development of electrostatic latent images on negatively charged surfaces is accomplished by applying a developer composition having a positively charged triboelectric relationship with respect to the colloidal silica. Additionally, in U.S. Pat. No. 3,893,935 there is described the utilization of certain quaternary ammonium salts as charge control agents for electrostatic toner compositions. There is also described in U.S. Pat. No. 4,298,672 positively charged toner compositions with resin particles and pigment particles; and as a charge enhancing additive alkyl pyridinium compounds and their hydrates, inclusive of cetyl pyridinium chloride.
Generally, the aforementioned prior art developer compositions are selected for use in developing electrostatic images wherein the toner image is fixed to a permanent substrate, such as paper, by contacting the paper with a roller, the surface of which is formed from a material capable of preventing toner particles from sticking thereto. In this process, however, the surface of the fixing roll is brought into contact with the toner image in a hot melt state, thus a part of the toner image can adhere to and remain on the surface of the fixing roll. This enables a part of the toner image to be transferred back onto the surface of a subsequent sheet thereby resulting in the well known undesirable offset phenomena.
To substantially eliminate offsetting, and more specifically for the purpose of preventing adhesion of the toner particles to the surface of the fixing roller, there have been selected certain types of rollers, the surface of which may be covered with a thin film of an offset preventing liquid such as a silicone oil. These oils are highly effective, however, the apparatus within which they are incorporated is complicated and costly since, for example, a means for feeding the oil is required. Also, not only do the silicone oils emit an undesirable odor, they can deposit on machine components causing toner particles to adhere to the oils. An accumulation of toner particles on machine components is troublesome in that the image quality is adversely effected, and further these components must be periodically cleaned and/or replaced adding to the maintenance costs thereof. The aforementioned offsetting problems can be substantially eliminated with the black and magnetic toner compositions as disclosed in U.S. Pat. No. 4,460,672. This patent, the disclosure of which is totally incorporated herein by reference, illustrates positively charged toner compositions comprised of resin particles, pigment particles, a low molecular weight wax material, and a charge enhancing additive. More specifically, in one embodiment the U.S. Pat. No. '672 patent discloses a positively charged black toner composition comprised of resin particles containing polyester resins, styrene butadiene resins, or styrene butyl methacrylate resins; pigment particles; a low molecular weight waxy composition, such as a low molecular weight polyethylene or polypropylene; and a charge enhancing additive selected from the group consisting of alkyl pyridinium halides, organic sulfonate additives and organic sulfate additives. Also, there is described in copending application U.S. Ser. No. 655,381, now U.S. Pat. No. 4,556,624, entitled Toner Compositions With Crosslinked Resins and Low Molecular Weight Waxes, the disclosure of which is totally incorporated herein by reference, positively charged electrostatic toner compositions comprised of a polyblend mixture of a crosslinked copolymer composition, a second thermoplastic polymer, pigment particles, a charge enhancing additive, and a wax component. The aforementioned compositions are useful for affecting the development of images wherein offset preventing liquid such as a silicone oil is not required. Accordingly, the compositions of the present application are similar to those illustrated in the copending application with the primary exception that there is selected for the present invention colored pigment particles excluding carbon black.
There, however, continues to be a need for colored positively charged toner and developer compositions which are useful in electrostatographic imaging systems. More specifically, there is a need for improved positively charged colored toner compositions, which can be selected for permitting the development of electrostatic latent images in electrostatographic devices wherein offset preventing liquids such as silicone oils are not required. There is also a need for colored toner compositions wherein imaging is accomplished with coated hard fuser rolls, and wherein substantially no offsetting results.